This invention relates generally to devices controlling the flow of fluid and in particular to devices for accurately controlling the flow of fluid without permitting the continuous flow of fluid from the inlet port to the outlet port of the device.
The devices of the prior art for controlling the volumetric flow of fluid from an inlet port to an outlet port comprised diaphragm pumps and piston reciprocating pumps which achieved their variation in volumetric fluid flow through the use of variations in length of the pump stroke and frequency of reciprocation. In general, the devices for varying the length of pump stroke in the prior art devices were generally complicated mechanically and not too accurate in their adjustability. When adjusted to very small stroke volumes, for example, 0.1 microliter, the backflow or regurgitation of check valves influences output in a random fashion that renders flow inconsistent. So too were the techniques for varying the reciprocation frequency.
Such devices may be accurate enough for large volume flows but for very small quantities of fluid flow as is required for the infusion of medications to a patient, their accuracy leaves much to be desired.